The above sentence in Duff's textbook is translated by Duff as, "Why should we listen to the teacher?"

But, stripped of context, couldn't the sentence also be translated as, "What should we listen to from the teacher?"

Given that the sentence has no context, could it be interpreted in more than one way? Or is Duff's translation the only proper one?

ἁκουειν means "hear"; it commonly construes with an accusative of the content heard and a genitive of a person from whom one hears the content. "Listen (to)" or "pay attention (to(" is commonly προσέχειν (with implicit νοῦν) and a dative of the person.

I would expect Duff's sentence, as it's written, to mean "What will we hear from the teacher?" It's true enough that τί can be used in the sense "why, for what reason", but if that's the intention, it would be clearer to use "διὰ τί".